Prestigious — that’s how everybody from Gov. Cuomo on down is describing the award that Assembly Speaker Sheldon Silver will pick up next month in Chicago from the National Conference of State Legislatures.

What’s left unsaid is the name of the august honor — the William M. Bulger Excellence in State Leadership Award. And there’s a good reason for everyone’s silence — or maybe omerta is a better word.

For almost 20 years, as president of the Massachusetts state Senate, South Boston’s Billy Bulger was the most powerful politician in his state. The source of his immense clout? His brother, James “Whitey” Bulger — the most powerful gangster in the city of Boston, a cocaine-dealing FBI informant currently charged with 19 murders.

Politicians trembled before Billy, though he was barely 65 inches tall. The late Boston Mayor Kevin White was once asked the source of William M. Bulger’s power. “If my brother threatened to kill you,” the mayor replied, “you’d be nothing but nice to me.”

In the Bulger family, one hand washed the other. With Whitey threatening anyone who went after his little brother, Billy likewise took care of his older sibling.

State troopers who targeted Whitey saw their careers ruined by transfer or forced retirement. The guy who fired him from a no-show janitor’s job at the courthouse got his pay frozen for five years.

In 1988, Billy Bulger decided to gut a local housing court after the presiding justice refused to hire one of Bulger’s cronies. Gov. Mike Dukakis could have vetoed the brazen payback, but he too was terrified of the Bulgers.

At the time, he was the Democratic nominee for president. The judge asked a reporter, “How can Dukakis stand up to the Russians if he can’t stand up to a corrupt midget?”

But nothing ever stuck to the Corrupt Midget — he and Whitey had the local FBI in their pocket, especially one John “Zip” Connolly, yet another Southie native.

Zip was always on call whenever any honest cops began closing in on either brother. Soon Zip owned two houses and a boat, even though he often left his FBI checks, uncashed, in his desk for months at a time.

When Zip finally moved on (into a six-figure sinecure at a state-regulated utility), Billy delivered the testimonial at the FBI retirement dinner.

“He’s the personification of friendship,” Billy said. “He’s a splendid human being. He’s a good pal.”

Zip now lives in Florida: He’s serving a 40-year sentence for second-degree murder in a 1982 gangland hit in Fort Lauderdale.

All good things come to an end: In 1995, Whitey was indicted in a massive racketeering case. He went on the lam — and Billy soon left the state Senate to become president of the University of Massachusetts.

Then Congress started investigating the Bulgers’ sinister control of the Boston FBI office. The House Committee on Government Reform subpoenaed Billy to testify in 2002. Asked if he knew where his brother was hiding out, he took the Fifth.

Gov.-elect Mitt Romney ordered Billy to testify if he wanted to keep his $359,000-a-year state job. A few months later (after being immunized), Billy reappeared before the committee. The first question was: Did you know what Whitey was doing for a living all those years?

“I had the feeling that he was, uh, in the business of gaming and, and, uh,” he stammered. “Whatever. It was vague to me but I didn’t think, uh — for a long while he had some jobs, but, uh, ultimately, uh, it was clear that he was not, uh, um, being, um, uh, you know, he wasn’t doing what I’d like him to do.”

Three months later, Romney forced Billy Bulger out as UMass president. (He got a $900,000 severance check, plus a $200,000 annual state pension.) His brother remained on the lam, second behind Osama bin Laden on the FBI’s Most Wanted List.

Finally, last year, the FBI found Whitey living in Santa Monica and took him back to Boston to stand trial.

Billy attended Whitey’s first hearing. A TV crew cornered him leaving the courthouse and asked what it had been like to see his psychopathic brother after all these years.

Billy thoughtfully considered the question for a moment. “These are,” he finally said, “unusual circumstances.”

Perhaps Speaker Silver will feel the same way as he accepts the prestigious William M. Bulger Excellence in State Leadership Award.